Webelo Thanks! Unfortunately, that change also didn't help.
Since NGINX upgrade to 1.2.7 web forms aren't working and I've been looking to fix this for last two weeks, I don't know if this is NGINX bug or something else. I posted same questions on their forum asked on support chat - still no help!
I don't know if it's possible to downgrade NGINX to previous version and how, would that even fix the issue?
I will most likely have to re-install my server with Apache because it's widely used where if there's an issue I'm sure there's a solution available faster.
ISPConfig 220.127.116.11p1 | Debian Wheezy | BIND | Dovecot 1.2.15 | Apache 2.2.16 | MySQL 5.5 | PHP 5.4.4-14